As you know the gang led by T. and Blackie systematically destroyed Mr. Thomas's house and they even locked him in the bathroom.

Based on this, if I were Mr. Thomas, I would be thinking the following:

First, I would be very upset that these boys would have the audacity to destroy my house. I would think that these youths are depraved and have no respect for society, people, and private property.

Second, I would be sad that the gang of youths would actually do this very thing. I would think that World War II and all the bombings in London created a generation of youths that only knew destruction. Greene even intimates this point:

"Streaks of light came in through the closed shutters where they worked with the seriousness of creators - and destruction after all is a form of creation. A kind of imagination had seen this house as it had now become."